Cardiac Flashcards
What is a ventricular assist device?
Mechanical systems
Reduce the workload of the heart allowing the ventricle to rest, whilst maintaining cardiac output and perfusion of vital organs
What types of ventricular assist devices are there?
Left
Right
Biventricular
What are the indications for a ventricular assist device?
Acute heart failure as a bridge to recovery e.g. inn cardiogenic shock secondary to MI, viral cardiomyopathies, post cardiotomy
Chronic heart failure resistant to medical therapy - as a birdge to transplant
How is a ventricular assist device placed?
The LVAD typically inserts from the left atrium to the ascending aorta and an RVAD from the right atrium to the main pulmonary artery
Requires sternotomy
The short term devices are normally extra-corporeal and pts need to stay on ICU. Longerterm devices are often intra-corporeal and pts can be discharged therefore improving the quality of live.
What are the pros and cons of ECMO instead of a ventricular assist device?
VA-ECMO doesn’t require a sternotomy and supports both the heart and the lungs
Useful in short-term situations e.g. myocardial stunning that should resolve within 2-5 days
Cons - ECMO is resource intensive, technical and requires meticulous attention to limb perfusion, cannulae position and oxygenation and is unsuitable for longer-term use.
The cost of an LVAD is relatively inexpensive
What are the contraindications to VAD insertion?
- Cardiac: biventricular failure in > 65s, reversible causes of heart failure, severe aortic or mitral valve lesions
- Resp: FEV1 < 1L, Fixed pulmonary hypertension
- Renal: long-term dialysis, Cr > 265
- Hepatic: cirrhosis, fixed portal hypertension
- Vascular: AAA > 5 cm
- Neuro: recent or evolving stroke, unable to manage device
- Haem: unable to tolerate anticoag
- Psych
- Micro: severe sepsis, immunodeficiency
- Malignancy: metastatic cancer
- Nutrition: BMI > 40 or chronic severe malnutrition
What are the most common complications post ventricular assist device insertion?
- Bleeding
- Tamponade
- RV failure
- Fluid overload
- Vasoplegia
- Haemodynamic instability
- Hepatic dysfunction and ileus
- Infection
Describe electrical activity in a myocyte
Negative resting membrane potential (-80 mV)
Stimulation above threshold opens voltage-gated ion channels resulting in an influx of cations and rapid depolarisation of the cell
After depolarisation a plateau phase occurs, maintaining a positive membrane potential through the influx of calcium ions
This plateau phase allows for a refractory period, preventing repolarisation until the entire myocardium has depolarised
Repolarisation
What is the rate of spontaneous discharge of the AVN
60/min
What are the causes of cardiac conduction defects?
Anatomcal - myocardial ischaemia, MI, cardiomyopathy, post cardiac surgery, valvular heart lesions
Physiological - electrolyte abnormalities, endocrine, hypertension
Pharmacological - AV blockers, alpha agonists
What is the classification of conduction defects?
First degree heart block
Second degree heart block - Mobitz 1 (Wenkebach), Mobitz 2
Third degree/complete heart block
Bundle branch block - left, right, bifascicular, trifascicular
What is first degree heart block?
Conduction delay between the SA node and the ventricles
What are the ECG features of first degree heart block?
RP interval prolongation > 0.2s
What is second degree heart block?
Occurs when not all impulses are conducted to the ventricles
Mobitz 1 May be associated with RCA occlusion/inf infarction.
What are the ECG features of Mobitz type 1?
Progressive lengthening of the PR interval followed by failure of conduction of an atrial beat
What are the ECG features of Mobitz 2?
Intermittent failure of electrical conduction through the AVN.
May occur at random or in a pattern e.g.2:1
Associated with an anterior MI
Often progresses to complete heart block
What is complete heart block and what ECG changes occur?
Complete disruption of the conduction between atria and ventricles
Ventricular conduction is initiated by pacemaker cells within the ventricles.
ECG show no association between the p wave and QRS waves
The morphology of the QRS depends on its origin - may be narrow or broad
May occur temporarily secondary to intense vagal stimulus.
What does the ECG show in RBBB?
RSR (M) pattern in V1 and V6 shows a typical W with a small initial downwards deflection
ST depression may be seen in V1-3
QRS axis is usually normal
Can be normal or represent underlying cardiac disease.
What happens in LBBB?
It results in a complete reversal of direction of depolarisation within the septum. This alters the direction of the initial deflection of the QRS complex in every lead
V1 - W pattern. V6 M pattern
Indicates the presence of cardiac disease
What is bifascicular block?
- RBB + anterior fascicle of left bundle. ECG shows RSR in V1 + LAD
- RBBB + posterior fascicle of left bundle. ECG shows RSR in V1 with excessive RAD
What is trifascicular block?
Bifascicular block plus first degree block
